Regenerative furnace



Aug. 1, 1933. M. H. MCEWAN REGENERATIVE FURNACE Filed April 2o, 1929 2Sheets-Sheet l IL.|II|| lllvllll:

2 Sheets-Sheet 2 M. H. MCEWAN REGENERATIVE FURNACE Filed April 20, 1929ug. l, w33.

Patented Aug. 1,1933 i `*Matthew Hamilton McEvvan, Loudon, VEnglandVvapplication April., 29,1929, serial No. 256379,99@

in Great Britain April 28, '1928 j lThisinvention*relates to"regenerative; furnacesQljsuirli "as coke ovens'lo'r the like, aclaptedf'tog be* inedl Witnrich Ygas or 1ea`nj ,gas at xviii.' AIS is .Wellknowngininrmswith lean gas it .is

usual topreheat both-the lean gas-'and thev com:

, bastion air, Whereas in ring with rich gasV only v Whether {tlie'fvrefgener feo , stanc i l 'raamt/satten Lprovides a constratohiwheiefin'lthe sarneinlet'valvel governs the admission the 'Y'combustionfair ',is brehe'ate, `v 'and in" iur-l naces vadapted,forfijring byvyeithermethod', itjis tlieV fpraetice to provdefone vorVmore of .the re` generators associated; Yvvitn"the'v kfurnace VW'itlrmeans-vvliereloy theycan be s-:tlppliexl with air,

orjwitlr leang'as a'tvgill.V The reversal 'rneo'ha-A nisin ofnaregenerator Y generally comprises 'La box;

o'rftlc't 'in perniaiient'communication vvthjthe regeneratorV andliaving ,an inlet valve govern ing 'the'-admission;` to 1 thejregenerator Soi gaseous Viinidlto'loe preheatedl and anjexfrianstfvalvegov'- A btistion tofthewastega ;iu'e,1eitlier one'valve place offfeoinloiistion; l lInjtlie oasevr ofaI Y regen-` erater adaptedior-preireailg `air or lean" gas Vwat will, ,it is'4 the practise"y toprovidel separate* inlet' valves-fior governing the passage to the`regen# erator oi `air `angl, lean gas, respectively, 'the jap-r .vpropriete {inletl alve being operate@V at teaeh ilringfif W' eng'j "asisfnsoallyfthefcase, f'orin-f in coke oven batteries), the Ainlet'f'valves ofja'l number ofvregenerators' 'arefoperate byaoi'rlrrion fin'eohanisin'jf either separate mecharaisin' re t requiredforthe 'gas Aandr 'air' vinlet" -vallv "rlnieans {inustbe provided forrenden one inlet vvalve .of Fa#regenerator andi inopeiw` ativeviniespeet'oi thelotlner inletyvalvef toa regeneratoioftlie appropriategaseoti's fluid (zeitrferf arriver' lean gas) indepenclently of theVvmdeoijiring'.operatinAeording to the respectively."

invention-.tire niet valve Controls communica-l tionf'loet'weieregenerator ancla box Vor'tlieY like :ha "altre-controlled.communications f vrithzasource of lair, land-fa source loi lean gascation-r arene? 'withfthe sources, of' airand learrgas are'set,inlaocordance with-the mode? .gf adopteolf-so thatfeither'airor leangasy isx admittegiJ-fto' 4tljie A y box, said valves,r when or'j istraversed by 'waste t *isf-desiredy to change tineA mode off :nei valvesControlling Qeonimtinif 1x1l Clarins, RC1. 1er- 144:57

once set, do not require manipulation aslong' as the particular mode offiring is inoperation',

vvhilstr-tne inletvalve is operated` at each reversal of theregenerator, regardless of Whether the latter is to preheat air or leangas, v

In' the preferred construction, the looxispro-A vided, on the side ofthe inlet Valveren'iote from the'inteior of the boxgwth anAv extensionin which the Waste-gas valve Vis accommodated', so that theloose,extensonpand the several;valves` oonstitntejan ndivdualunit. Sucha unit corr1- 'prises a casing having two compartments; come'inunioation betweenkvvhioli is eontrolleclby the inlet valve;"one`compartrnent having aj valve oon-Y trollerl communication with theWaste-'gasflue and loeing` permanently in oornmunication'with theregenerator, Whilstk the other compartment hask valve@controlledjAcommunications 'Withj sourcesV ofair and lean gas, respectively. Conveniently kthe mechanismnfor operating (the valves is mounted ony theeasingjano. forms-'apartofl the unit. t, ,n In order to avoid thepossieilityfof admitting looth'-gas,anclair to the box or cn'npartrnent`si# multaneously', the invention comprises a'olevice, which lockseither' the gas valve ror tnellair valve lin tlieelosed position as iongaetlife other valve isopen. Oneforrn lof construction oompiisesa slidehavinggslots capable vofferig'agirre"oonstriot Aed portions oftliersternslofV the valves `(orgth'eirV eqnivalents, suoli jas theoperai-,ingl handle 'ofl La slidingVA plate) `the varrangeur'ent beingsuch4 that "at all times one oriothervalve is looked iniolosedposition'anrl cannot be Vreleased vvloilstV theother valve fis openffAny risk oflaolrnitting'ajmixture changing overa'regenerator from aperiod oiY gas an'dfai'r to the aliot' regenerator is thereby *oflefeiveshearfrom combustion producers f vDeIOC Qlprelieating airf'orvfuel gases, orvice'V versa, it is desirable `that there shouldloe;ariinter5,`

val betweenl the operationl ofV the Waste-'gas "valve" and the operationof the inlet valve, andaeonstriiotionv in accordance'vvith' the iinvention may loe feojnbietl with a reversal fnechanisin wherein thetvvo valves 'are' operated by asingle actuatingV rneeiianisrritviiiehSilit"ornaticallvv `allows for "the afoifesaiclinteival. For example,theyalesmay bejaetiiatel by amLrotatablefmenioer stroll "as a leveradapted to be' rotated by ,af suitable A.111; 1ec`l1'aposite dire onQatintervals corresponding With nisml'rstn onedirection anclftlien yin the"op-f thegpreheatmgffand lfieatiritg; periods; tliev initialrv Y stageoi rotation ofthe, rneznber deterinining'- flee1V closingo `one valveand a subsequent" stage' of the rotation determining the opening of theother valve.

Practical considerations require that the in-V terval between theoperation ofthe valves in changing over a regenerator should be lesswhen air is to be preheated than when gas is to be preheated, and theinvention further comprises a. construction .whereby the actuating.mechanism may operate to open one valve through either of two devices,which come into operation at different intervals after the operation ofthe other valve. Conveniently'the position of the locking slidepreviously referred to determines the interval between the operation ofthe valves, whereby it is possible to ensure automatically that theinterval between the operation of. the-inlet and waste-gas valves shallbe suited to the vparticular medium which is to be preheated. l

TheA accompanying drawings illustrate an apparatus constructed inaccordance withthis invention,. 1

` Fig. 1 being a side elevation,

Fig.` 2 a horizontal cross' sectionfon the line 2--2'of Fig. 1,

Fig. 3 a. vertical section on the line 3--3 of rigranci Fig. 4 verticalsection onv` the linef44-4 of Fig. l, with some parts omitted. f

Referring to Figsfl and 2, theapparatus comprises a box or casing ldivided by a vvvall2 into two compartments '3 and 4 communicating by wayof a port inthe wall 2 closable bythe -inlet valve 5. The compartment 3Vis permanently in communication With a regenerator (not shown) by wayof a duct 6'and canbeplaced in communication with the waste-gas flue byway of a duct 7 closable bymeans of the waste-gas valve 8; the duct 7may contain a suitable-damper 9 operated by va handle`10. Thecompartment 4 may be placed-in communication at will either with theatmosphere byway 'of a port 11 which can be closed-by a slidingplate 12operated by means of a handle 13, or withthe gas main (not shown) by'wayoi a port S14 which canbe closed by means of .aA screw-downyalve 15voperatedby rotation of a wheel 16- mounted on the valve-stem 17,whichpissupported in guides 18 in a bracket 19` v'mounted onthecasingy 1. In the construction'-'illustrated, Vthe valves areset for thepassage of waste gases from the regenerator to the'vwaste-gas flue, thatis to` say, the. waste-heat'lvalve 8 is ,open an d the inlet valve 5 isclosed. In/ Changing ov'er kthe regenerator from', a VVheating period,which fis traversed-v by'hotlgases`to a pre-heating period, in which it'is traversedby air or gas to be preheated, the valve 8isclosed,andthevalve 5YV is opened (by mechanismpres'entiytopedescribed) whilst either the slide 12 o rltlie valve 15- is-opened, de-Vpending upon whetherair orgas is tobeadmitted, by way ofcompartments4and 3, to the regenerator. 'A v i Forthepurpose of ensuringthat'yalve 15 and plate 12 cannot simultaneously be open, there isprovided a lockingdevice comprising a slide 20' vslotted atk 21 and 22and movable vlongitudinally in' guidways 23 yin. thefbracket 19. TheWidth of the slots 21, 22 is lessthanthe normal diameter ofthevalve-'stem'l'l and handle 13, but the latter have constrictedportions24,25 which are capable of entering the slots 2 1'A and 22 respectively.1

The dimensions of theslide vand. slots and the` position'of theconstrictions on the handle13 andY valve-stem V1 7 are ysuch thattheslots can only,

and its extreme left position (as in Fig. 2) in which the constriction25 is positioned in an enlarged recess 26 at one end of slot 22, whichrecess is capable of accommodating the portion of the valve stem 17below the constriction 25. In the extreme rightv position, it will beseen that when the plate 12 is raisedand an unconstricted portion.

of the handle is brought opposite to the slot 21, the slide 20 cannot bemoved to disengage slot 22 from the constriction 25 so that thegas-valve 15 is locked in closed position; similarly, in the extremeleft position the action of opening the valve l5 brings an unconstrictedportion of the valvestem into the recess26, 'and prevents movement ofthe vslide 20 to disengage the constriction 24 from the slot 21, vthuslocking the plate 12 in closed position. The slide is moved by'means ofa handle Y27.

The reversal mechanism forchanging over the regenerator from apreheating period to a heating period and vice versa' is actuated by alever 30 .pivoted'at one' end in bearings 31 in a bracket 32 on the'casing 1, and connected at or near its other end to a rod or rope 33(common to the reversal mechanism of a number of regenerators) which ismoved at suitable intervals alternately in one direction and in theother direction by a suitable mechanism (not shown). The Waste-gas valve8 issuspended by a chain 34 (Fig. 1) attached at apoint on rtheperiphery of a quadrant 35 integralwith the lever 30, and is operated byrotation fof the .lever30 about its axis. The inlet valve5is suspendedby a chain 36.s ecured on the periphery of a quadrant 37 mounted on asleeve 38 which can rotate freely on a shaft 39 carried in bearings48;the shaft 39 is itself rotated by movement ofthe lever `30 vthrough theintermediary of a link 40 pivotally attached to the lever and to an arm41 extending from the shaft 39. f

`In the position of lever 30 as shown in Figs. 3 -and 4, the rod andlever are their extreme right position, .andthe waste-gas valve 8 israised from its seat, the inlet valve 5 being closed.

VVillienit is desired to change over the regenerator to a preheatingperiod, the rod 33 is moved inthe direction of the arrow (Fig. 3)whereby the lever 30 and quadrant 35 are caused to rotate in thecounter-clockwise direction andthe waste-gas' valve 8 is lowered on toits seating. Before the lever 30. reaches the end of its travel (shownapproximately in dotted lines in Fig. 4) a boss 42 4(Fig. 3) mountedadjustably on the link 40 comes into Contact with and bears on anarm43`formed integrally with a member 44vv rotatably mounted cna support49,' thc further'movement of the lever30 to theend of its travel thuscausing rotation oi the arm 43f and the member 44. By means of an arm 45Vformed integrally with the member 44, an arm 46 secured tothe sleeve 38and a 'link 47 pivotally connected with the free ends ofarms 45,A and46rotation of the member from its seating. The dimensions andarrangement of the several parts are so selected that a.-

suitable intervalelapses between theclosing of rod',` retraction of Vthe`bossf- 42 permits 'the by suitably-adjustingthe position of the boss`42 1 on thc-linked In. the reverse movement 'of the inlet' valve todescend on to its` seating before the v'vvastcgas valve 8 opens.Y

-Tneconstruction valso embodies a clutch mechanismwhereby rotation oithe shaft `39 maybe `19 transmitted directlyto-thesleeve38; VThe clutclrmechanism comprises airnember -keyedto the shaft 39 so asvtofvr'otat'e'-i-,herewithY and free to` slide longitudinally v'alongvthe shaft, 'and aplate 5l secured to the sleeve 38 and having anar'uatel5 slot 52 (Fig.v 4l) concentricV With'the sleeve. The

clutch is closed by slidingthemernber 50 alongY the shaft 39 to cause astud 53 carried vby 4the membery 5GY to Venter "the yslot 52, whilst thelever 30 is inthe position shown in Figs. 3 and 4. 5 Rota- 123 tionV ofthe lever 1in the counterclockwise direc- 25l when further rotation ofthe shaft is transmitted elapsesl between` rotationlof the sleeve 38 issomewhat greater than wir.

Ation ris transrnittedV to the fshaft' 39 -and clutch4 memberi3d-through links 40, 4211. Theginitial roy-- tation ofthe-shaftgcaiises the stud 53' toV travel in the arcuate slot v52 untilit reaches the end 54,

to thev sleeve-"S8 and quadrant 37 through `the Ychit-ch mechanism,whereby the inlet valve-5 is; n raised nironiitsseating. The distanceoftravel of the stud 53 inthe slot 52 is such that,v when 3U theclutch-is closedfthe clutch mechanism' takesy precedence of thebossandarin mechanism' (42 and 43)" which operates.r as previouslydescribed when the clutchis open and is inoperative when thel clutchVisv closed, and` that? a desired interval theactuation of thc-`wastegasand'itnlet lvalves 8 and 5. Itwillbe seen 'that the l rotationV ofthemember 44 is somewhat magniiied in tstransmission through VVthe arms 45,46 and linkli'?V to the sleeve 38; that is to say, the angular thecorrespondngangular rotation of the member 44;: By-suitablydirnensioning'the "severalv partsit `is possible to arrange tlifattheinlet valve substantiallyithe s 'ame travel whether actu- 1-"-ate`d'thronghjthe bossand arm mechanism or through the clutch mechanism. 1 J

` The Vclutch isjconveniently controlled oy-'the movementl oftlielockingfslide 2O.'V` For -thi'spur- (pose,V Lthe slide carriesajbraclet@ Vto which is tliegas `valve15^irees the clutch. 1 Y

' itwvill be'seenthat, whether the clutch mechay isjopen ,or closed, theWastegas valve 8 ie inlet' valve 5 both` derive theirgmovement V'therotation of the lever 30 about itsV pivot.

V`naee,1 sncnas a cokeoven vortlie like', *adapted to box'liavingjcommunications with a source of ail" and' a so'nrce 4offlean y'gasrespectively, valves conm v' nmnihications,adevice cooperat?and'adaptedto maintain Welling' Said thin iully describedthejnature ofAthe ngthesarne into practical eicct,4 I clairn:-' Apparatus iercontrolling the supply4 of gasnf'd to ja yregenerator oi` avregenerative iur long as the-other oi said valves is open,r and-Van thebox and the regenerator and governing the admission to theregenerator oithe lean gas-or"l air admitted to the box.- f- Y v .2. Apparaus forcontrolling the supply Tof* Vgaseous fluid to a regenerator oi `aregenerative fur` nace, suchY as a coke oven-or the like, adaptedto befired byrich gas orby lean gas, comprising 'af casing divided intotwocornpartments, communications between one Acompartment and sources ofair and lean gas, respectively, valves controlling saidy communications,a device cooperating with said valves'and adapted to maintaineither `ofvsaid valvesloclged inl closed position as long` as the other of saidvalves is open, communicationsA between the other compartment and theregen-v kerator and a wastev gas flue, respectively, awastegas valvecontrolling communication between the said'compartinent and the wastegas flue, a confi-v munication betweenthe two cornpartments,Yandmunication.y Y y 3. Apparatus ior controlling the supply oi gasecusiluid to a regenerator of a regcnerativeifur nace, such as a coke ovenVor thelike, adapted to be fired byv rich or by lean comprisingA av boxhavingcommunications with a sonrceor air and a source of lean gasrespectively, valves controlling said communications, a slide having aninlet valve controlling the last-named com-f slots capable of engagingparts oirsaid! valvesso as to lool; either-valve in closed position,yandl so positioned anddimensioned thatlwhen in lockingl engagement witheither valveyit is Apre-1;:

vented from 'disengagement therewith vas long-kas the otiier valve isopen, and an `inlet valve con-' trolling communication betweenthe boxandthe Vregenerater and-governing-v the admission to the' n the leanAgas or air admitted .tol the box. Y "l i. controlling the supply ofgas`r rcge'nerator of 4 Apparatns for cous 'filuid to Aaregeneratoi"'of'afregenerative furnace, such as a' coke ovenA or `the"like,adapted-`.to be iiredby'rich gasor by leanfgas, coiriprising a casingdivide'dinto two comoartrnents,y com# rnuriications'L between Y onef-cornpartment and sources oi `air/and lean gasfrespectivcly, valvescontrolling said communications, a slide "having-l slots capable oiVengaging partsof said#valves1v sotas-to lock leitl'ier--valve in' closedposition,-andV so positioned and dimensioned that; when in lockingYengagement Ywith either valve,fit is 'prevented fromdisengagement'therewithas longfaa theV other valve open,communicationsbetween? the other compartment and the regenerator 'andinlet valve controlling communication between Y a waste-gas iiuerespectively, av -wa'stel gas valve' controlling communication betweenthesaid corni' partment and the waste gas fdue,V a communica-' tionbetween the two'coinpartments, and aninletl valve controlling thelastnan-ledv communication.

5,v Apparatus for controllingthesupply of gae-l? cous iiuidto aregenerator'of a regenerative 'fur-" nace, such'as a coke oven orthelike, adaptedtoV be fired Vby rich gas ror *by lean. gas, comprising!abox having valvecontrolled communications!" witlra Ysource of, air andasource tlean gas:v respectively, anV inlet'valv'e controlling communicationsvr between the box and the regenerator and governing theadmission'to the regeneratorof Ilean `gas or air'` supplied to` the box,a waste? gas valve controlling communication between the iregenerator'andgaivaste ilue, anda revers lf mechanism for'aetnating theinletandwaste gas"y valves, ivliicli'mechani comprises a Vinem`adaptedftorotate between two extreme poste V5150"' andjmeans whereby theearlier stage of the rotation from either position to the otherdetermines the closing of one of said valves and a later stage of thesaid rotation determines the opening of the other of said valves.

6.; Apparatus forcontrolling thesupply of gaseous fluid to a regeneratorof a regenerative furnace, such as a coke oven or the likeyadapted (5.0vil to lbe red by rich gas or by lean gas, comprising a box havingvalve-controlled Vcommunications with a source of air and a source oflean gas respectively, an inlet valve controlling communication betweenthe box and the regenerator and,y governing the admission to theregenerator of .lean gas or air supplied to the box, a waste gas valvecontrolling communication between the regenerator and a waste gasflue,and a reversal mechanism for actuating the inletv and waste gasvalves, which mechanism: comprises a' member adapted to rotate betweentwo extreme positions, means whereby rotation of said member actuatesonegof said valves, an arm l,rotatable about a pivot, and means wherebyrotation of said arm actuates the other of said valves, lsaid member i'and saidarm being so positioned that the earlier stage of the rotationof the -inember from its extreme position in which the valve actuatedthereby is open towards its otherextreme position causes a part or' themember to move into "contact with said arm, and the further rotation ofthe member causes rotation of the arm so as to open the-valve actuatedthereby. V'7. Apparatus for controlling the supply o gaseous iuid to aregenerator of a regenerative furnace, such as a coke oven or the like,radapted to be fired by rich gas or by lean gas, comprising' a boxhaving valve-controlled communications with a source of air and a sourceof leangas, respectively, an inlet valve controlling communilcationbetween the box and the regenerator and `governing the admission to thelregeneratoryof lean gas or air supplied to the box, a waste gas valvecontrolling communication between the reerative at kdiierent instantsduring the rotation' of the Amember from its extreme position in whichthe valve actuated thereby is open towards Yits other extreme position,and means whereby rota-r tion of the member is imparted to the shaft byeither of said transmission means.

-8. Apparatus for controlling the supply of gaseous iluid toa-regenerator of a regenerative furnace, such as a coke oven o1:` thelike,-adapted to be fired by rich gas or by lean gascompris ing va boxhaving valve-controlled communica- -tions with a source of air and asource oflean gas, respectively, an inlet valve controllingcommunication between the box andthe regrenerator and governing theadmission to the regenerator of Y lean gasv or air vsupplied tothe box,a `waste Y gas valve controlling;communication between the regeneratorand a waste gas flue, and a reversal mechanismvfor actuating the inletand waste gas valves, which mechanism comprises a member adaptedtofrotatebetween two extreme Lpositions, means whereby rotationof saidmem- -v ber actuatesone of said valves, a rotatable shaft, means wherebyrotation of said shaft actuates the other of said valves, an armrotatable about a pivot, means for imparting rotation of said arm tosaid shaft, said arm and-,said member being so positioned that theearlier stage of the rotation of the member vfrom its extreme positionin which the valveactuated thereby is open towards its other extremeposition causes a part of said member to move into contact with saidarmand the further rotation of the member causes rotation of the arm,and a clutch mechanism adapted to transmit rotation of said membertosaid shaft and operative, when the clutch is closed, before the partor^ said member comes into contact with said arm.

9. Apparatus for controlling the supply of gaseous fluid to aregenerator of a regenerative furnace, such as a coke oven or the like,adapted to be fired by strong gas or by lean gas, comprising a box-having communications with a source yof air and a source of lean gasrespectively, valves controllingr said communications, a slide havingslots capable of engaging parts of said .valves as to lock either valvein closed position, and s o positioned and dimensioned that when-inlocking engagement with either valve, it is prevented from disengagementtherewith as long as the valve is open, an inlet valve controllingcommunication between the box and the regenerator and governing theadmission to the regenerator of the lean gas or air admitted to the box,a waste gas Valve controlling communication between the regenerat'or anda waste gas ilue, a reversal mechanism forv actuating the inlet andwaste gas valves, which mechanism comprises a member adapted to rotatebetween two extreme positions, means whereby rotation of said memberactuates one of said valves, a rotatable shaft,

'means whereby rotation of said shaft actuates the other of said valves,an arm rotatable about a pivot, means for imparting rotation of said armyto said shaft, said arm and said member Ybeing SOY positioned that theearlier stage ofthe rotation ofthe member from its extreme position inwhich the valve actuated thereby is open towards its other extremepositionl causes a part of said memberto move into contact witlrsaid armand the further vrotation of the member into contact with said arm andmeans whereby` theclosing of the clutch is determined by movement ofthevv slide intolocking engagement with the leangasvalve. i Y l0.Apparatus for controlling the supply of gaseous fluid toa regeneratorofa regenerative furnace, such as a coke oven or the like, Vadapted to bered'by a strong gas or by lean gas, comprising a casing divided into twocompartments, 'communications between one compartment and sources ofairand lea-n gas respectively, valv es controlling said communications, aslide havingslots .capable of Aengaging parts of said valves so as tolock either valve in closed position and so positioned' and dimensionedthat when in locking engagement with either valve, it is prevented fromdisengagement therewith as long as the other vvalve is open,communications between the other compartment and the regenerator and awaste-gas nue respectively, a wastegas Valve controlling thecommunication between the said ,compartment and theN waste-gas flue,

a communication between the two compartments,r an inlet valve.controlling the last-named com-` munication, a reversal mechanism foractuating the inlet and waste-gas Valves, which mechanism comprises amember adapted to rotate between two eXtreme positions, means wherebyrotation of said member actuates one of said Valves, a rotatable shaft,means whereby rotation of said shaft aetuates the other of said Valves,an arm rotatable about a pivot, means for imparting rotation of said armto said shaft, said arm and said member being so positioned that theearlier stage of the rotation of the member from its extreme position inwhich the Valve actuated thereby is open towards its other extremeposition causes a part of said member to move into contact with said armand the further rotation of the member causes rotation ofthe arm, and aclutch mechanism adapted to transmit rotation of Vsaid member to saidshaft and operative, when the clutch is closed, before the part of saidmember comes into contact with said arm, and means whereby the closingof the clutch is determined. by movement of the slide into lockingengagement withv the lean-gas valve.

11. Apparatus for controlling the supply of gaseous fluid to aregenerator of a regenerative furnace, such as a coke oven orrthe like,adapted to be iired by rich gas or `by lean gas, comprising a casingdivided into two compartments, a valve-controlling communication betweenthe compartments, an outlet in one compartment communicating with theexterior and adapted to be connected to a waste-gas flue of aregenerative furnace, a valve controlling said outlet, reversalmechanism adapted to actuate said Valves to place the said compartmentin communication alternately with the other compartment and,

'through said outlet with the exterior, said re- Versal mechanismcomprising a member adapted to rotate between two extreme positions andmeans whereby the earlier stage of rotation from either of saidpositions to the other determines the closing of one of said Valves anda later stage of the said rotation determines the opening of leo@

